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A quick review of interesting research on living things from the last month.

When they aren’t walking or feeding, flamingos stand on one leg and sleep. They can maintain this pose for far longer than we can and don’t need to shift their weight to the other leg. Using two dead birds, researchers examined how their long legs held up their body weight. When flamingos stand on one leg, muscles and ligaments lock into place so they don’t strain their muscles and burn energy. Standing on two legs makes them unstable, requiring their muscles to burn more energy. The one-legged pose also gives greater stability to the birds, reducing sway.

Cowbird moms pay attention to the size of eggs in the nests they choose for egg-laying. Inset: Two cowbird eggs (the two larger ones in the nest of a northern cardinal. Credit: Loren Merrill; Inset photo by Scott Chiavacci

Brown-headed cowbirds are like cuckoos, laying their eggs in other birds’ nests. Until now, researchers thought these mothers dump their own eggs in any unattended nest. A new study says that’s not true. Mother cowbirds choose nests that would give their own chicks a better chance of survival. They lay their eggs only after the host species has laid at least one. This gives them a chance to estimate how successful their own chicks will be under foster care. If the host bird species is large, cowbirds plump for nests with smaller than average eggs. Not only would this mean their own eggs will incubate successfully, the host’s small chicks wouldn’t compete with cowbird offspring for food and space. However, if the host species are smaller, cowbird mothers aren’t finicky about egg size. These birds seem capable of making sophisticated judgments.

A colony invests a lot to raise queen ants. Every summer, these sexually mature winged insects soar from their natal nests to mate and start new colonies. If they develop in the wrong season or if there are too many queens, the colony would waste its resources on them. Worker ants don’t let that happen by bullying and biting the larvae to remain workers. All grubs in a colony are identical – legless and white-bodied – making the ‘royal’ larvae hard to distinguish. How do worker ants find them?

Researchers from North Carolina and Arizona State universities smeared juvenile hormone from queen larvae of Indian jumping ant (Harpegnathos saltator) on worker and male larvae. They released the ‘princess pheromone’ even though males can’t develop into queens. Within 24 hours, worker ants recognised them as ‘royal’ larvae and bit them to prevent their development as queens.

Dark-eyed juncos are socially monogamous, i.e., males and females share a territory and raise their offspring together. But male birds that are already in a relationship cannot resist the temptation to hit it off with an unattached female. Researchers placed a caged female and watched if they courted her in the same manner as bachelors. They discovered males that are spoken for woo surreptitiously. The little grey birds are quick to approach the female, sticking within 5 metres radius of her with their feathers puffed erect compared to bachelors. They also jump from perch to perch more often and sing fewer songs quietly to not attract the attention of others. Surprisingly, the males carry on with their flirting even within sight of their irate partners. Although these females dove at the cage and chased their fickle mates away, the relationship didn’t dissolve. The researchers say social context causes variation in birds’ courting repertoire and birdsong as much as body condition and hormones.

Coping with loss

Vampire bats drink the blood of large warm-blooded animals. If they don’t find a meal, their mothers and sisters regurgitate to feed the starving bats. Such reciprocal feeding isn’t restricted to family alone. They generously donate some of their meals to non-relatives. Why be nice to others?

A common vampire bat mother with young. Credit: Uwe Schmidt

Researchers removed a few captive vampire bats, starved them for a night, and returned them to the enclosure. Before releasing them, they removed their kin. The larger their social network, the more they got to feed. When a starving vampire bat returns to its real world colony, there’s a chance its mother or sisters may have gone to roost elsewhere. Since its family circle is small compared the number of friends it can make, vampire bats engage in ‘social hedging’ as insurance against starvation.

Great tits cope with loss of a flock-mate by building stronger ties with others. Credit: Molly Harwood

While the bats build social relationships to cope with loss, birds deal with loss by strengthening their social bonds. Researchers caught 23 great tits and held them in captivity for a weekend and watched how the others coped. The ones who lost flock-mates hung around feeding stations longer and associated with others more. Great tits respond to missing buddies by forging tighter connections with others. The loss didn’t cause a breakdown in their social network as predicted earlier.

How long do orangutan infants nurse? Observing behaviour while their mothers swing between rainforest trees is difficult. Primatologists weren’t the only ones struggling to find the answer to this simple question. Researchers also sought to know from fossils how long Neanderthal infants nursed.

In 2013, a new technique offered a breakthrough. Teeth bear the imprint of a milk diet. Minerals deposit in layers on enamel and dentine. One such mineral is barium that’s chemically like calcium and is mainly absorbed from mothers’ milk. This makes it an accurate indicator of the duration of breastfeeding.

After their first birthdays, orangutan infants start eating fruits, leading to a corresponding drop in barium levels in their teeth. As they grow older, they rely on their mothers’ milk during periods of scarcity. By analysing the teeth of four young orangutans that had been shot dead decades ago, researchers from Australia and the US arrived at an astounding answer. A Bornean orangutan suckled until it was more than eight years old while a Sumatran one hadn’t weaned completely even at the time of its death at 8.8 years of age. No other primate nurses for this length of time.

Banded mongooses rear their pups as a community. Mothers give birth at the same time and suckle each other’s offspring. If adult mongooses identify their own young, they could provide more care. But they can also harass other pups, even going to the extent of killing them. When the young are old enough to emerge from the den, they each pick an adult to be their own escort. These attendants feed, groom, and protect their wards, even though they may not be related. The authors said males alone looked after the pups in a paper published two years ago. But in this study, they say male pups gravitate towards adult males and females stick to females. Females tend to escort pups if they had given birth that season so they have a higher chance of looking after their own. But males attend pups if they are related to others in the group, making the youngsters their half-siblings.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.

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Acknowledgment

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